154 TRANSACTIONS AND PROCEEDINGS OF THE [Sess. lxvi. 



parent. It is, I take it, the looseness of this union of 

 chromosomes, and the ease with which it may be undone 

 at the reduction and sex-determination, which explains 

 why a child, for example, often bears more likeness to a 

 grandpaient than to a parent. 



As to the rest of the diagram, this relates to the deter- 

 mination of sex, and to the final phases of oogenesis and 

 spermatogenesis. With the exception of the portions 

 relating to the determination of sex, the data concerning 

 oogenesis are taken, as will be recognised, from Boveri's 

 well-known figures. Of course, the embryo is not supposed 

 to be hermaphrodite ; both sexes being included in one 

 diagram merely for purposes of convenience. 



For fuller details concerning the determination of sex, 

 the reader may be referred to my recent communication^ on 

 this subject. In the upper part of the diagram, attached 

 to the fifty-fifth primary germ-cell, the probable course of 

 oogenesis in the skate is shown. With the final division 

 of the oogonium into two oocytes, o.c, the determination of 

 sex is depicted as happening in the formation of male 

 oocytes and female ones. These enter the period of growth, 

 and then pass on to ripen. Lower down, for comparison, 

 the spermatogenesis of Paludina, with its two kinds of 

 spermatozoa, is represented after the statements of Meves. 



The portions of the diagram appended to the fifty-fifth 

 and twentieth primary germ-cells can naturally be applied 

 to any of the remaining primary germ-cells, other than that 

 which goes to form the embryo. 



In conclusion, what Weismann has termed the 

 germinal track nowhere here touches the cells of the 

 embryo. Neither, as we have seen, does it really lie 

 within the asexual generation, or phorozoon. It is along 

 a line of unicellvdar organisms, which pass a portion of 

 their life-cycle between one conjugation and the succeeding 

 one within a sterilised individual, formed by the self- 

 sacrifice of one for the good of the rest. 



As revealed by the diagram, throughout this line of 

 unicellular organisms, which are ever such, until one or 

 other of them gets into the cul-de-sac of embryo-formation, 

 there is a direct morphological continuity of germ-cells. 



^ See " Anat., Aug. 1902," and for the full memoir, " Zool. Jahrb., 

 Morph. Abtheil, 1902." ' 



